12月和2月热带太平洋海温与东亚水汽输送关系的年代际变化机制

Interdecadal Oscillations and Underlying Mechanisms Linking Tropical Pacific Sea Surface Temperature to East Asian Water Vapor Transport in December and February

利用1950~2019年NCEP/NCAR大气再分析资料、NOAA海表面温度资料以及ERA5垂直积分水汽通量资料,分析了12月和2月热带中东太平洋海温与东亚水汽输送关系的年代际变化。结果表明,12月东亚上空经向水汽输送与热带中东太平洋海温的相关性在1980年代中期之前较弱,1980年代中期之后二者呈显著正相关;2月二者关系在1950~1970年和1990~2010年呈显著正相关。12月二者关系年代际变化的主要原因是热带太平洋海温通过太平洋—东亚(PEA)遥相关型和环北半球遥相关型对东亚水汽输送的影响在1980年代中期之后增强;当热带中东太平洋海温偏暖(冷)时,影响PEA遥相关型和环北半球遥相关型,导致东亚自南向北的水汽输送异常增强(减弱)。与12月不同的是,2月二者关系在1950~1970和1990~2010年主要受PEA遥相关型影响。而在1971~1989期间,2月二者关系受环北半球遥相关型影响;当热带太平洋海温偏冷(暖)时,影响环北半球遥相关型,导致东亚经向水汽输送异常增强(减弱),该机制可以部分抵消PEA机制对东亚水汽输送的影响,导致二者关系在此期间不显著。此外1990年之后,热带印度洋海温对12月和2月东亚经向水汽输送的影响增强,在12月热带印度洋海温主要通过“开尔文波—埃克曼辐散”效应影响东亚经向水汽输送,而在2月主要通过印度洋上的沃克环流影响东亚经向水汽输送。

Using NCEP/NCAR reanalysis data,ERA5 vertical integrated water vapor flux data,and NOAA monthly mean SST(sea surface temperature)data,the interdecadal variations in the relationship between central and eastern tropical Pacific SSTs and East Asian WVT(water vapor transport)in December and February from 1950 to 2019 were investigated.The finding reveals that the correlation between East Asian meridional WVT and central and eastern tropical Pacific SSTs in December was weak before the mid-1980s,becoming significantly positive afterward.In February,the correlation was significantly positive during 1950–1970 and 1990–2010.Interdecadal variations in the relationship between East Asian meridional WVT and central and eastern tropical Pacific SSTs in December stem from the increased influence of Pacific–East Asian(PEA)teleconnection and Northern Hemisphere circumglobal teleconnections on East Asian meridional WVT,driven by tropical SSTs after the mid-1980s.The PEA teleconnection and Northern Hemisphere circumglobal teleconnection would induce anomalous southerly WVT over East Asia,corresponding to warm SST anomalies in the central and eastern tropical Pacific.Unlike December,the relationship between the two factors in February was primarily modulated by the PEA teleconnection during 1950–1970 and 1990–2010.However,from 1971 to 1989,East Asian WVT was influenced by the circumglobal teleconnection in the Northern Hemisphere,corresponding to cold SST anomalies in the central and eastern tropical Pacific.This resulted in an insignificant relationship between the two factors during 1971–1989,as the above mechanism counteracted the effect of the PEA teleconnection.Furthermore,the impact of tropical Indian Ocean SSTs on East Asian WVT in December and February increased after 1990.In December,East Asian WVT was modulated by the Kelvin wave-induced Ekman divergence mechanism,while in February,it was influenced by the Walker circulation over the Indian Ocean,corresponding to warm SST anomalies in the tropical Indian Ocean.